1. Field of the Invention
The present invention relates to windshield wipers having improved pressure distribution between the wiper lip and the windshield thereby resulting in improved wear and wipe characteristics.
2. Description of the Prior Art
Many attempts have been made in known windshield wipers to attain a more uniform pressure distribution along the portion of the wiper which bears against the windshield. Some attempts centered on preventing a non-uniform pressure distribution by concentrating on the manner in which the wiper was connected to the supporting superstructure -- a major cause of poor pressure distribution. Other attempts centered on compensating for the non-uniform pressure distribution caused by connection of the supporting super-structure to the wiper, or by the curvature of the windshield. In Mainka U.S. Pat. No. 3,473,186, a windshield wiper is disclosed which comprises a head (upper portion) having base portions and a lower portion having flanges, a front or body and a lip. A neck connects the upper and lower portions and is sufficiently flexible so that under wiping action over a windshield, the downstream flange contacts the downstream base portion to thereby exert pressure on the lip to maintain it in contact with the windshield. The flanges are used to control blade layover and corresponding blade pressure against the windshield. To avoid excessive pressure between the lip and the windshield below the areas of connection of the wiper to the supporting superstructure, it was disclosed to provide flanges whose width varies along the length of the blade in a plane which is parallel to the windshield surface, the width being reduced in zones below the said areas of connection. Such variation in flange width reduces the resistance of the front or body to deformation therebelow in response to engagement of the lip with the windshield, thereby enabling the lip to undergo more pronounced flexing below the said areas. Excessive pressure points were thereby reduced below the said areas of connection due to the increased flexing of the lip and increased layover of the lip and front and the corresponding reduction in force between the reduced width flange and a corresponding base portion. For the improved distribution of pressure in the aforementioned patent, it is essential that there be layover of the body (front) and contact with the base portion during wiping, otherwise there can be no reduction of force against the flange by the base portion with a corresponding reduction in excess pressure of the lip on the windshield.
Two common problems associated with wiper pressure distribution are known in the art as streaking and patching. Both can adversely affect driver vision. Patching is to be distinguished from streaking in that much larger areas are involved. Patching commonly originates from excessive lip and front layover and hydrodynamic action which permits water to pass between the lip and the windshield.
The present invention primarily increases useful wiper life, also reduces patching and streaking, and otherwise improves wiping action by reducing excess pressure concentration between the wiper and a windshield below the areas of connection of the wiper to the supporting superstructure. The foregoing advantages are realized substantially regardless of the degree of blade layover and regardless of contact between the upper and lower portions.